Process of vulcanizing rubber



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Patented 5e35, 1939 t I UNITED s'rl 'T -s mism- 01m 1 i aocnssorvfizlzizmeauan Norman R. Wilson, Belleville', in annuir. Lang.

Jersey City, IN. 1., alsignors to Bare Hetal'l'bod- Ilcts Company, Bclleviiie, N.- I., a corporation of e New Jersey .No Drawing. Application 8,1987. I r Serial No. 151,809 4 '28 Claim. (61260-780) This invention relates to rubber vulcanization, stances will retard the low temperature (say. V ,and comprises a process of making rubber artibelow 230' 1".) vulcanization of rubber mixes, escles wherein "scorching" of quick-vulcanizing pcially in the case of mixes containing certain rubber mixes during the milling, storage or moldtypes of organic accelerators,'without unduly re- 5 ing is prevented by the addition to the mix of tarding the high temperature vulcanization 5 certain retarders; and the invention includes, (around 275 F.).-'I'hisclass of retarders includes also, such retarders, and the improved rubber the halogens, chlorine, bromine and iodine, andproducts resulting from the use of such process I compounds containing such halogens in "r vailand retarders. able" form, such as, h ypochlorites a r 1 d l i-chloro m In the manufacture of molded rubber goods WCompounds containing halogeiisi'in l the crude rubber is milled with the desired fillers, available form are distinguished from the mesulphur and accelerators for vulcanization. Ortallic or organic halides by the fact that, in genganic accelerators are used, not only to reduce the eral, the former have xldizing properties where; time of vulcanization, but also to give the vul- 4 as the latter do noty m'ipe cliicmhe formercanized product physical properties that could will liberate either the free halogen or hyponot otherwise be obtained. The milling not only halous acid when treated with an acid as eviproduces an intimate mixture of the various indenced by the fact that when these are treated gredients, but also makes the mass plastic and, with acidified potassium iodide free iodine is libtherefore, moldable. vulcanization, on the other erated; whereas the halides do not liberate iodine 29 hand, makes the mass elastic and destroys the when added to acidified potassium iodide. We plastic properties. The aim of the rubber manuhave found that the compounds containing the facturer is, therefore, to complete the molding halogens in available form produce new and before any appreciable vulcanization has ocunexpected results as vulcanization retarders. curred. As the mix includes all the ingredients Fluorine and fluorine compounds are not suitnecessary for vulcanization, it often happens, 88-: able, and for that reason the halogens coming 95 pecially when powerful accelerators are used, that within the scope of this invention are those hav-' partial vulcanization occurs so early that it inter-. ing an atomic weight over 35. iereswith the completion of the molding process. While the exact reason for the retarding action t In such cases the mix is said to be "scorched". of halogens is not known, it is believed that vul-- vulcanization of rubber is a chemical reaction canization is a reaction of the chain type and a with a high temperature coeflicient. The temthat the halogen continually removes one of the f: perature of the mix during milling and prior to essential elements of the chain so that the reac- J N vulcanization is frequently not greatly below that tion velocity is extremely small until all of the of vulcanization. If the compound contains a halogen has been consumed, when the chain repowerful accelerator the temperature coefilcient is action is free to continue inv its normal manner frequently not high enough to prevent scorchand at substantially its normal velocity. There- '4... ing v fore, there is a limit to the amount which should a As a result, it is desirable to have amix which be used. The amount of each of these retarders will not vulcanize to any appreciable extent at necessary to give the desired results lies within 200 to 230 F. during the time normally required certain limits which vary according to the other 49 H 7' to mill and mold and whichwillsubsequently vulingredients present in the mix as well as the V canize rapidly at around 275 to 300 F. processing methods and conditions. In the case of rubber cementa'which may not .In certain rubber compounds there are limitabe used for six months or so after preparation, tions in the use of certain accelerator combinapremature vulcanizatio may occur, even at room tions to give the desired physical properties in 45 temperature. the'flnal product because scorching occurs. The g -The object of the present invention is to preuse of a suitable retarder woulddecrease those vent premature vulcanization in either of these limitations. Hence, the use of a retarder not Y situations, or situations similar thereto. only makes the manufacture of rubber articles we have found that a certain class oi submore fool-proof, but also makes it possible to I (2) N-halo compounds:

2 airnaoi I obtain a finished product superior to that obtained with the same compound without the retarder.

In the prevention of scorching it is desirable to I their effect on the tensile strength of rubber, our e retarders may be divided into three main groups:

(1) Hypohalites, such as hypochlorites and like bromine and iodine compounds, both inorganic and organic, and the free-halogens,

- chlorine, bromine and iodine. a

(a) N-halo compounds which are derived by the simple addition of a halogen to, or the substitution by a halogen for one or more of the hydrogen atoms of, an organic compound whose aqueous solution has a pH less than 7.5.

(b) N-halo compounds which are derived by the simple addition of a halogen to, or the substitution by a halogen for one or more of the hydrogen atoms of, an organic compound whose aqueous solution has ,a pH more than 7.5.

Some of the retarders of groups (1) and (2-a) when used in amounts suffici'ent to give really substantial retardation reduce the tensile strength somewhat. Those of group (2-b), on the other hand, do not impair the tensile strength and in some cases even raise it.

While the broad group (2) is divisible as to efiect on tensile strength according to the acidic and basic character of the compound from which they are derived, that does not appear to be, true of group (1). Thus, those of group (1) formed from basic compounds like hypohalites, have under some conditions reduced tensile strength. While the exact explanation of this difference between groups (1) and (2) is not known, it is believed to be related to the fact that in hypohalites the halogen is more loosely combined i as than is generally true of the group (2) compounds, or may be due to poor dispersion of the retarder.

N-monochloro-guinone imida I The first of these is derived from a basic compound, while the compound from which the second is derived, owing to its oxygen content, is acidic in character. The first raises or at least does not reduce the tensile strength of the vulcanized rubber, while the secondlowers it somewhat.

A second example is given by the following:

N-chloro-melamino- The first is deriv ew from'anacidic product.

One. of the most suitable members of group (Z-b) is the aliphatic compound NN'-dichloroazo-dicarbonamidi-ne, CzNsHaCla, whose probable structural formula is:

- sic and the second N=N\ NCl=C c=Noi 7 Na, Na, This compound will hereafter be referred to as'N. D. A..

Another very satisfactory aliphatic compound is ,the above mentioned N-chloro melamine or the corresponding dichloro compound.

Among group (2'-b) retarders are N-bromophthalimide, N-N-di-chloro-quinone-bis-aminoguanidine, and N-chloro-benzamidine.

Other group (2-a) retarders are, chloramine- B, chloramine-T, dichloramine-T, 1,4-N-N-dichlor-diimino-naphtho-quinone-2-sulfonic acid,

swc'cin-chlorimide, ethyl-N-chlorlmino carbonate, an N-chloro -acetyl urea.

. At 220 F. or lower temperatures vulcanization proceeds so slowly with inorganic accelerators of the type of calcium oxide, litharge or magnesia, that it is rarely necessary to use retarders to prevent scorching during milling and molding.

The organic accelerators are much more powerful and it is with them that our retarders find their chief field of usefulness. .With these organic accelerators our retarders work best with certain types of accelerators.

For the purposes of the present invention, the organic accelerators now in use may be divided into two main groups: v w

(1) Those which contain a-SH or either a -S or S.S- group, formed by substitution .in or condensation of a mercaptan.

(2) Those which do not. 1

Most of those accelerators included in group (1) may be subdivided as follows:

1-A. Salts of, thio acids, such as zinc butylxanthogenate and dinitro-phenyl ester of dimethyl-dithio-carbamic vacid. Two of-the sim- ,7 plest acids of this group are dithio-carbamic acid,

" NHaCS -SH, and xanthic acid,

-l- -B. Mercapto-thiazoles, or mercaptan derivatives of I o s v s V 110 N HC cn H" (in I 7 HP I l Thlo ortlio monazole. Thio meta monazolo.

Accelerators of this" group include mercaptobutyl-amine, heptaldehyde-anlline and paraor di-ortho-tolyl-guanidine.

I as

tolyidine-acetaldehydeaniline condensation product. Y I

2-D. Guanidines, such as diphenyl-guanidine s-s. Thiurams, such as tetra-methyl-thiuram-mono-sulphide,

' cm s s ./NPl-S&N cm

and tetra-methyl-thiuram-disulphide, 4 cm .s s cm cm on, 9

. tained with accelerators of all the above types.

With a very few members of the above groups,

such as the condensation product of butyr-aldehyde and mono-butyl-amineof group 2-0, the retarding eflect under the conditions of'test was negligible. In no case, using calcium hypochlorite, was low-temperature vulcanization accelerated.

It is believed that with hypocholorites there is a retarding effect in all cases, although in some instances it may be neutralized by anaccelerating eil'ect produced by the decomposition .prodnets of the hypochlorlte. The accelerators with which the retarding effect was negligible were all y relatively slow acting, so that the activating effect of the decomposition products' of the hypochlorite would be greater than in the case of the more rapidly acting accelerators.

With N. D. A., eifective retardation occurs only with accelerators of group (1), so that it is more specific than the hypochlorites. The

. cause of this diflerencc in action between hypoch1orites and N. D. A. is not known. It is be-' lieved, however, that N. D. A on giving up its chlorine yields an amino compound which activates accelerators of group (2) more strongly than do the corresponding products of hypochlorites. Hence, with accelerators of the group (2) types used alone, N. D. A. produces an acceleration effect greater than the retarding effect due to the chlorine. However, that does N. on

not appear to be true where a'group (2) accelerator is used in conjunction with a group ('1) accelerator to give amuch greater acceleration than can'be obtained by either accelerator alone. For example, N. D. A. has been found to have a marked retarding effect in the case of the combination of any of the following accelerators of group (2) with mercapto-benzo-thiazole of group Thio-carbanilide, Hexa-methylene-tetrannne,

. Acetaldehyde-amine,

2-D. Dihenyl-guanidine,

2-E. Tetrwmethyl-thiuram-disulphide,

iect of the amino compound on a given accelerator seems to be less when the action of the latter is already activated by another accelerator.

As a class, halogens'of atomic weight over and compounds containing such halogens in available form appear to act as retarders in the case of all of the above types of organic accelerators, although in some cases it is necessary to add another type of accelerator to overcome the tendency of the decomposition prodnets of the retarder to activate low-temperature vulcanization.

As an example of a suitable mix using N. D. A. as the retarder, the following is given.

Pale crepe 100 Cliil'stone whiting 100 Zinc oxide 5.0 Antimony sulphide 10.0 Sulphur 2 Benzo thiazyl disulphide .4... 1.0 Diphenyl guanidine 0.125 N. D. A 0.25

The above mix can be subjected to temperatures of about 230 F. or thereabouts for 35 to 40 minutes before scorching occurs."

The relationship between the content of retarder and the length of time the above mix may be maintained at 230 F. or thereabouts before it begins to scorch is indicated by the following lllustrative table:

Percentage N. D. A

i There is some slowing up of the time at which Percentage with different accelerators, retarders, temperatures, etc., widely difierent be obtained.

It is characteristic ofour retarders that they substantially completely inhibit vulcanization for a time, after which vulcanization proceeds at a rapid rate, instead of permitting vulcanization to begin almost immediately at a reduced'rate.

numerical results will The retarder, such as alkaline earth hypgchlorjtemaybeadded toa ac o ru rinamill tion retarder, without materially'aflecting vulcanization at 275 to 300F. This master-mix or chlorinated rubber may be added to the other constituents of the final mix in such proportion as to give one-tenth to one part of calcium hypochlorite to each 100 parts of pure dry rubber, or such other proportion as may be desired in the. final mix.

Organic hypochlorites, such as butyl h chloritefma'ffi usedf'everal of such compounds.

'fifich as butyl hypochlorite, are too volatile to incorporate in the usual milling operations. They to alkali hyp%hlorites which are too unstable to be added in d y form to a rubber mix.

may, however, be added to rubber cements or latex or similar. rubber suspensions and. thereafter exert their retarding action. The same applies when the free halogens, chlorine, bromine and iodine, are used, they may be added in the form or a carbon tetrachloride solution to a solution of rubber in benzene, containing vulcanizing in-- gredients, in the .proportion of around 0.2 to 0.25 percent of the halogen on the dry weight of rubber.

The free halogens or hypochlorites may also be added to latex or other aqueous suspension of rubber to produce a chlorinated rubber which.

may be used as a retarder in the preparation of rubber mixes. What is claimed is:

1 The-process of treating rubber which comprises subjecting a rubber mix containing an or-. ganic accelerator and a halogen with an atomic which would tend to cause a greater degree of scorching in the-absence of said halogen, and

then subjecting m vulcanizing temperature.

2. The process or making rubber articles, com- I prising adding to a'rubber mix an organic accelerator and a halogen with an atomic weight over 35 in available form to retard the action of thef. accelerator at milling temperatures,-milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vulcanizing temperature. a

3. The p'ocess of making rubber articles, comprising adding to a rubber mix an M erator and an N-halo com d of a halogen with an atofific, weight over 35 in available form to 1 retard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to temperature.':'

4. The process of making rubber articles, comprising addingto arubber'inlx an organic accelperature. weight overv 35 in available form, to conditions.

erator and an N-chloro derivative of an organic compound which contains chlorine in available form and whose aqueous-solution has a pH more than 7.5 to retard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vulcanizing temperature: x

5. The process ofmaking rubber articles, comprising adding to a rubber mix an organic accelerator and an N-chloro derivative of an aliphatic organic compound which contains chlorine in available form and whose aqueous solution has a pH more than 7.5 toretard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic, milled material to the desired form, and then subjecting it to vulcanizing temperature.

6. The process of making rubber articles, comprising adding to a rubber mix an organicaccelerator and a derivative of melamine containing available chlorine to retard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vulcanizing temperature.

7. The process of making rubber 'articles,.c'om- Drisingadding to a rubber mix an organic accelerator and a hypochlorite to retard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vulcanizing temperature.

8. The process of making rubber articles, comprising adding to a rubber mix an organic acceI eratorand calcium hypochlorite to retard the actionoi the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired l'orm, and then subjecting it to vulcanizing temperature.

9. The process of making rubber articles, comprising adding to a rubber mix an accelerator selected from the class consisting of compounds containing the groups SH and S- and compounds containing the groups SH and SS- derived from a mercaptan, and an N-chloro com.-

molding the plastic milled material to the desired pound containing chlorine in available form .to retard the action of the accelerator at milling temperatures, milling the mix to render it plastic,

form, and then subjecting it to'vulcanizing tem- 10. The process of making rubber articles, com

prising adding to a rubber mix an accelerator selected from the class consisting of compounds containing the groups -SH and S-- and compounds containing the groups --SH and derived from a mercaptan, and NNf-dichloro azo dicarbonamidine to retard the action of the ac-- celerator at milling temperatures, milling the mix to render it plastic, molding' the plastic milled ing it to vulcanizing temperature.

' material to the desired form, and then subjecte f the thio acid salt type and NN-dichloro azo dicarbonamidine to retard the action of the accelerrender it plastic, moldingthe plastic milled mate- ,rial to the desired form, and then subjecting it to vulcanizing temperature. 1

azo-dicarbonamldine to retard the action of the ator at milling temperatures, milling the mix to 12. The process of making rubber articles, com- 1 2,171,901 acceleratorat milling temperatures, milling the mix to render it plastic, molding the plastic milled of the (ii-substituted guanadine type and a halo-- gen with an atomic weight over in available form to retard the action of the accelerator at milling temperatures. milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vul-- canlzing temperature.

14. The process of making rubber articles, comprising adding to a rubber mix an accelerator of the thiazine type and NN'-dichloro-azo-dicarbonamidine to retard the action of the accelerator at milling temperatures, milling the mix to render it plastic, molding the plastic milled material to the desired form, and then subjecting it to vulcanizlng temperature.

15. A rubber vulcanization retarder, comprising a halogen with an atomic weight over in available form.

16. A rubber vulcanization retarder, comprising an N-chloro derivative of an organic compound containing chlorine in available form and whose aqueous solution has a pH more than 7.5.

17. A rubber vulcanization retarder, comprising an N-chloro derivative oi. an aliphatic organic compound containing chlorine in available form and whose aqueous solution has a pH more than 7.5.

18. A rubber vulcanization retarder, comprtsing NN'-dichloro-azo-dicarbonamidine.

19. A rubber vulcanization retarder, comprlaing a derivative of melamine containing available chlorine.

20. A rubber vulcanization retarder, comprising a hypochlorite.

21. A rubber product obtained by subjecting a mix containing an organic accelerator and a halogen with an atomic weight over 35 in available 15 term, to conditions which would tend to cause a greater degree of scorching in the absence of said available halogen and subsequently vulcanizing 1 the mix.

22. A rubber product which has been vulcanized m in the presence oi an organic accelerator and a hypochlorite. 7

23. A rubber product which has been vulcanized in the presence of an organic accelerator and an N-chloro derivative of an organic com- 35 

